Transparent Interconnect of Lots of Links (Transparent Interconnect of Lots of Links, TRILL) is a protocol applied to Routing Bridges (Routing Bridges or RBridges, RB). TRILL is executed in a Data Link Layer (Data Link Layer), i.e. layer 2 of an Open System Interconnection Reference Model (Open System Interconnection Reference Model). It mainly integrates the advantages of bridges (bridges) and Routers (Routers) and applies Link State Routing (Link State Routing) technique to a Date Link Layer, which does not interfere with the work of Routers in an upper layer. TRILL comes into being in order to substitute for the Spanning Tree Protocol (Spanning Tree Protocol, STP). Comparing with STP, TRILL improves the support of unicast and multicast in Multi-Pathing (Multi-Pathing) aspect and decreases delay.
Although Spanning Tree Protocol always plays a critical role in an Enterprise Network (Enterprise Network) in decades, it can not meet some requirements at present, such as live migration of a virtual machine, bandwidth intensive real-time media application and aggregating network structure by network center bridging.
Rbridges executes an Intermediate system to intermediate system (Intermediate system to intermediate system, IS-IS) protocol to broadcast connection information to all Rbridges. As a result, each Rbridges can know all of the other Rbridges and their relations of connection. In this way, Rbridges is given enough information to compute an optimal path of a unicast to any network node and distribution trees may be computed for a frame of unicast or multicast and for an unknown destination address.
An End Station Address Distribution Information (End Station Address Distribution Information, ESADI) protocol is an option of TRILL, which is used for the learning of a terminal address and distributing a terminal address information to a remote end, and which is realized through extending type-length-value (type-length-value, TLV) of IS-IS.
The message header of a TRILL message is shown in FIG. 6.
When a unicast message is sent, an RB which receives the message first is an ingress RB, which is responsible for performing TRILL encapsulation. The ingress RB searches, according to a destination Media Access Control (Media Access Control, MAC) address, a last RB on a forwarding path, which is called an egress RB. The ingress RB treats the nickname of the egress RB as Egress Rbridge Nickname (Egress Rbridge Nickname), treats its own nickname as Ingress RBridge Nickname (Ingress RBridge Nickname), and puts them in a TRILL header. Each of the Nicknames (Nicknames) is a dynamically designated 16 digits and is used as the abbreviation of IS-IS identification of RBridges so as to achieve the effect of compact coding. A protocol for dynamically obtaining a nickname is executed among all the RBs. For a multicast or broadcast message, an egress RB nickname represents a distribution tree and the nickname is the root of the distribution tree. Ingress RB is responsible for choosing which tree to perform a multicast or broadcast forwarding. Once receiving a message, an intermediate RB (not the ingress RB and the egress RB) determines a layer 2 address of a next-hop RB according to the egress RB, treats the layer 2 address as a destination address of an external layer 2 message header, treats its own layer 2 address as a source address of the external layer 2 message header, and descends the value of a Hop Count (Hop Count). Although the external layer 2 message header changes with each hop, the contents of the original message (i.e. the internal message) do not change.
Shortest Path Bridging (Shortest Path Bridging, SPB) provides a similar function as TRILL. It spreads and advertises topologies and relationships of members of logical network by using IS-IS based link state routing technique and provides logical Ethernet on the traditional Ethernet architecture.
The encapsulation method of MAC-in-MAC is applied to SPB to encapsulate a client Ethernet frame to an operator Ethernet frame.
As MAC-in-MAC adds a service instance tag (instance tag, I-Tag) field, operators may distribute Quality of Service (Quality of Service, QoS) parameters and define a unique identifier (instance service identifier, I-SID) for a user by using the field. As a result, a unique I-Tag can be distributed to the flow of each client, and QoS can be executed according to client rather than Virtual Local Area Network (Virtual Local Area Network, VLAN).
SPB establishes a shortest forwarding path through a layer 2 IS-IS protocol. Edge bridges are the interfaces between clients' network and service providers' network, which are similar as RB devices in the TRILL. When an Ethernet message arrives at an edge bridge from a user equipment, this kind of equipment encapsulates a client Ethernet frame with a mac-in-mac frame header and inserts a Backbone destination MAC address (Backbone destination MAC address, B-DA), a Backbone VLAN ID (VLAN ID) and an I-Tag of the edge bridge corresponding to an associated destination address. A switch in a backbone network is responsible for using a pre-defined routing to forward frames in a network according to a Backbone VLAN identifier (Backbone VLAN identifier, B-VID). Switches in the backbone network adopting SPB are different from traditional Ethernet switches is that they do not adopt a STP method.
Although TRILL and SPB use different encapsulating formats, both of them have similar uses and methods, and both of them apply link state routing to a data link layer protocol.
An Address Resolution Protocol (Address Resolution Protocol, ARP) realizes a function of getting a physical address of a device through an Internet Protocol (Internet Protocol, IP) address. Under an IP network environment, each host is assigned an IP address of 32 digits, and the IP address is a logical address of identifying a host in the range of network. In order to transmit a message in a physical network, a physical address of a destination host must be known, and in this way, there is an address transform problem of transferring an IP address to a physical address. Taking Ethernet environment as an example, in order to transmit a message to a destination host correctly, an IP address of 32 digits of the destination host must be transferred, according to address correspondence, into an address of Ethernet of 48 digits, i.e. MAC address. In this way, a group of services in a network layer is needed to transfer an IP address to a corresponding physical address, and this group of protocols is ARP protocol.
Because of the use of TRILL and SPB, a problem brought by using STP in the original layer 2 network is overcome, which makes a layer 2 network of a larger scale, i.e. large layer 2 network, become to be possible. However, large layer 2 network brings other new problems. Since the enlargement of a layer 2 network, the number of network nodes increase. If a traditional ARP protocol is still used, an ARP request of each host is broadcasted in VLAN, and in this way, flows of broadcasting messages occupy too much bandwidth. Additionally, since edge RBs, i.e. RBs which connect terminal devices, need to store MAC information of all terminal devices, their MAC tables can be huge.